1. Field of the Invention
The present invention relates to a fan. More specifically, the present invention relates to a ventilation fan including waterproof and dustproof mechanisms.
2. Description of the Related Art
A ventilation fan such as an axial fan or a centrifugal fan typically includes an impeller having a plurality of blades, a motor arranged to rotate the impeller, and a circuit board for motor rotation control. Each of the impeller, the motor, and the circuit board are accommodated in a housing.
Depending on the environment in which a ventilation fan is used, water, dust, or the like may disadvantageously enter into the housing from the outside. If water or dust enters into the motor or the circuit board, this causes a problem in which the motor may break down, so that the ventilation fan cannot operate.
In view of such a problem, Japanese Laid-Open Patent Publication No. 10-191611 discloses a technique in which a stator portion of a motor and a circuit board are molded with a resin.
However, the technique requires extra time and cost necessary to form the resin mold, which thus leads to an increase the cost of the ventilation fan.
Japanese Laid-Open Patent Publication No. 2000-110773 discloses a technique in which a labyrinth structure is provided in a gap between an open-side end portion of an impeller cup and an open-side end portion of an outer wall portion of a motor supporter.
However, in the technique disclosed in Japanese Laid-Open Patent Publication No. 2000-110773, it is necessary to provide a cylindrical inner wall portion in the motor supporter and an annular flange in an open-side end portion of the inner wall portion in addition to the gap for constituting the labyrinth structure. These requirements cause the structure of the ventilation fan to become complicated.